Preparation of thermoset cycloolefin polymers via metathesis catalysts is a relatively recent development in the polymer art. Klosiewicz, in U.S. Pat. Nos. 4,400,340 and 4,520,181, teaches preparation of such polymers from dicyclopentadiene and other similar cycloolefins via a two-stream reaction injection molding technique wherein a first stream, including the catalyst, and a second stream, including a catalyst activator, are combined in a mix head and immediately injected into a mold where, within a matter of seconds, polymerization and molding to a permanently fixed shape take place simultaneously.
In the presence of a metathesis catalyst system, polymerization takes place extremely rapidly even at low temperatures. In fact, polymerization occurs so rapidly that it is not unusual for the monomer to polymerize to a solid immobile condition before the mixed streams can be transferred to the mold. To overcome this difficulty, Klosiewicz teaches the inclusion of a reaction rate moderator in the activator stream to delay the catalyst activation until the reaction mass is totally within the mold. The total time from mixing until polymerization is substantially complete is still just a matter of seconds. The present invention is concerned with a method of producing such a delay in polymerization with a different catalyst system than the one employed by Klosiewicz and one which requires fewer components than the prior art systems.
In the typical system, according to Klosiewicz, the catalyst component is a tungsten or molybdenum halide and the activator is an alkyl aluminum compound. The reaction rate moderator can be, e.g., an ester, ether, ketone or nitrile. The present invention does not require the addition of the reaction rate moderator when tin activator compounds are employed. More recently, in patent application Ser. No. 250,209 it was disclosed that the activator compound could be a dialkyl zinc compound.
Most strained ring non-conjugated polycyclic cycloolefins are metathesis polymerizable. These include, for example, dicyclopentadiene, higher cyclopentadiene oligomers, norbornene, norbornadiene, 4-alkylidene norbornenes, dimethanooctahydronaphthalene, dimethanohexahydronaphthalene and substituted derivatives of these compounds. The preferred cyclic olefin monomer is dicyclopentadiene or a mixture of dicyclopentadiene with other strained ring hydrocarbons in ratios of 1 to 99 mole % of either monomer, preferably about 75 to 99 mole % dicyclopentadiene.
The metathesis catalyst system is comprised of two parts, i.e., a catalyst component and an activator. The preferred catalyst component as taught by Klosiewicz has been a tungsten halide, and preferably a mixture or complex of tungsten hexachloride (WCl.sub.6) and tungsten oxytetrachloride (WOCl.sub.4). A different tungsten halide catalyst is used in the present invention.
The tungsten or molybdenum compound is not normally soluble in the cycloolefin, but can be solubilized by complexing it with a phenolic compound. Preferred phenolic compounds include phenol, alkyl phenols, halogenated phenols or phenolic salts such as lithium or sodium phenoxide. The most preferred phenolic compounds are 2,6-di-tert-butyl-p-cresol (BHT), 2,6-diisopropylphenol (DIPP), 2,6-dichlorophenol, t-butyl phenol, t-octyl phenol and nonyl phenol. The preferred phenolic compound for complexing the tungsten compounds in the present invention is 2,6-diisopropylphenol.
Recently, Basset et al. in The Journal of Inorganic Chemistry, Vol. 26, No. 25, pp. 4272-4277, (1987) and in European Patent Appl. EP No. 259,215, Mar. 9, 1988 taught the preparation of a tungsten catalyst having the formula ##STR1## where X is Cl or Br, n is 2 to 4, R.sub.1 is a hydrogen, alkyl group, phenyl, or an alkoxy group 1 to 8 carbon atoms in length and R.sub.2 is a hydrogen or a bulky alkyl group 3 to 9 carbon atoms in length. For example, the W(OAr).sub.3 Cl.sub.3 complex was produced through the reaction of WCl.sub.6 with 4 equivalents of 2,6-dimethyl or 2,6-diisopropyl disubstituted phenol in carbon tetrachloride. A mixture of W(OAr).sub.3 Cl.sub.3 and W(OAr).sub.2 Cl.sub.4 compounds is produced which may be easily separated due to the large difference in their solubilities in the reaction medium. The synthesized compounds were black solids (dark red-purple in solution), stable in air at room temperature, insoluble in pentane, hexane and alcohols but soluble in aromatic and chlorinated solvents. Basset et al. also disclose the preparation of a variety of other tungsten complexes. In the Basset et al. European application the use of a variety of cocatalysts or activator compounds was reported in the polymerization of dicyclopentadiene including SnR.sub.4, R.sub.3 Al, R.sub.2 AlX and RAlX.sub.2, where R is an alkyl group and X is a halogen. Although Basset et al. listed a variety of cocatalysts, the experimental results reported were with C.sub.2 H.sub.5 AlCl.sub.2 and (C.sub.2 H.sub.5).sub.2 AlCl. Applicant has found that the aluminum compounds do not provide an adequate exothermic polymerization reaction when used with the tungsten catalyst compounds of this invention to polymerize pure DCPD.
Sjardijn et al. disclosed in U.S. Pat. No. 4,729,976 that with their method, unlike prior art methods, it is not necessary to employ pure dicyclopentadiene monomer. Impure dicyclopentadiene is polymerized in bulk by tungsten catalysts in cooperation with either a trialkyl or triphenyl tin hydride complex, e.g. n-Bu.sub.3 SnH or Ph.sub.3 SnH. The preparation of two catalysts is taught in Examples 1 and 2 of the '976 patent, which are incorporated by reference herein, as follows:
Catalyst 1, WCl.sub.4 (DIPP).sub.2, was prepared by the reaction of 1 eq. WCl.sub.6 +1.85 eq. DIPP. Catalyst 2, WCl.sub.5 (BHT), was prepared by the reaction of 1 eq. WCl.sub.6 +3.0 eq. BHT. The tungsten catalysts disclosed by Sjardijn et al. are W(OAr).sub.2 Cl.sub.4 and W(OAr)Cl.sub.5. A desirable feature of the Sjardijn et al. invention is that it employs a tin compound such as trialkyl or triphenyltin hydride as the second component of the two component catalyst system. Such tin compounds are less sensitive to water and oxygen contamination than the aluminum compounds that have been used as activators in polymerization systems such as described by Klosiewicz.
However, it has been found that when the tin compounds of Sjardijn et al. (in particular, tributyltin hydride) are used with Sjardijn's Catalyst 1 or Catalyst 2 to polymerize pure dicyclopentadiene, there is almost instantaneously an extremely rapid gelation of the mixture and concomitant exothermic polymerization. A delay in gelation is necessary to prevent polymerization until the mold has been filled. In producing molded polymeric articles, it is preferred to use pure dicyclopentadiene monomer rather than the impure monomer used by Sjardijn et al. due to considerations of predictability of polymer properties.
This invention provides a process to employ Sjardijn et al's tin compounds and other activator compounds in a system in which gelation and polymerization are delayed for at least a time sufficient to charge the reaction mixture to a mold. Both the catalyst and activator compounds have improved stability with resistance to oxygen and moisture. The catalyst compounds used in this invention are easy to isolate, instead of being mixtures as are those found in the prior art. In addition, delays in gel and cure time are obtained without the need for addition of a rate moderator compound.